Smile

What is it about a smile that makes other people happy? Is it the fact that it symbolizes happiness or do we just like what it does to people's faces? I have been wondering this recently because Lee started to smile on Sunday. I couldn't believe how excited and happy I was that he was finally able to do that. He has smiled a few times since then, and each time I get so excited. It is strange to me that a baby's smile is so different from a grown-up's smile, and yet we think of the baby's smile as cute and we recognize that it is actually a smile.
I also think that it is amazing that one of the very first things that a baby learns how to do is smile. Why is that do you think? Could it be that it is because that is what the baby sees most often? Or is it because those are simply the first muscles to develop? Is the baby actually happy, or is he just mimicking what he sees? I don't know why I am thinking so much about Lee's smiling, maybe it is hormones or maybe it is because he is my last baby, but I sure do love the fact that he is smiling now.